Exothermal effects in the thermal decomposition of [IrCl₆]^2--containing salts with [M(NH₃)₅Cl]²⁺ cations: [M(NH₃)₅Cl][IrCl₆] (M = Co, Cr, Ru, Rh, Ir)

[M(NH₃)₅Cl][IrCl₆], M = Co, Cr, Ru, Rh, and Ir, were proposed as single-source precursors for bimetallic alloys. Their thermal decomposition in inert and reductive atmospheres below 700 °C results in the formation of nanostructured porous Ir_0.5M_0.5 alloys. Salts decompose with a significant exothermal effect during the first stage of their thermal breakdown in an inert atmosphere above 200 °C. The exothermal effect gradually decreases in the series: [Co(NH₃)₅Cl][IrCl₆] (1) > [Cr(NH₃)₅Cl][IrCl₆] (2) > [Ru(NH₃)₅Cl][IrCl₆] (3) > [Rh(NH₃)₅Cl][IrCl₆] (4); [Ir(NH₃)₅Cl][IrCl₆] (5) does not exhibit any thermal effects and decomposes at much higher temperatures. To shed light on their thermal decomposition and the nature of the exothermal effect, DSC-EGA, in situ and ex situ IR, Raman, XPS and XAFS studies were performed. A combination of complementary techniques suggests a simultaneous ligand exchange and a reduction of central atoms as key processes. In [Co(NH₃)₅Cl][IrCl₆], Co(iii) and Ir(iv) simultaneously oxidise coordinated ammonia, which can be detected due to a significant exothermal effect and the presence of Co(ii) and Ir(iii) in the intermediate product. The appearance of Ir-N frequencies demonstrates a ligand exchange between cations and the [IrCl₆]^2- anion. Salts with Cr(iii), Ru(iii), and Rh(iii) show a much lower exothermal effect due to the stability of their oxidation states. Salts with Rh(iii) and Ir(iii) demonstrate a high thermal stability and a low tendency for ligand exchange as well as decomposition with exothermal effects.